I have owned an AHP. Worked great. Mine was a 2014 and didn't have AC frequency adjustment. I sold it and bought and an Everlast DV200. Great machine as well.
I've been curious about the same thing. A 30 second Google search revealed this;
https://club.craftsman.com/projects/gas-pump-build
And this;
https://www.fordbarn.com/forum/showthread.php?t=109360
Long time lurker, first time poster...
I have the 2014 version of the AHP AlphaTig. After upgrading to a CK torch and an SSC pedal, I'm loving it.
Doug